Compressed gas seismic energy generator

ABSTRACT

A compressed gas gun for generating a seismic pulse in water. It has a floating-action piston controlled by an auxiliary piston for releasing a compressed gas charge suddenly. It also shapes the discharge gas pattern in the water to reduce secondary bubble pulse action.

C Unlted States Patent 1 [111 3,750,097 Havlik et al. July 31, 1973 [54]COMPRESSED GAS SEISMIC ENERGY 3,369,627 2/1968 Schempf 181/.5 HGENERATOR 3,433,202 3/1969 340/8 R 3,434,562 3/1969 Johnson l8l/,5 H[75] Inv nt rs: J hn J- lhvl k; Billy ll- T h 2,967,048 3/1961Fontaine.... l81/.5 H of Houston, Tex. 3,540,543 11/1970 Bays |81/.5 H

[73] Assignee: Texaco Inc., New York, NY.

Primary Examiner-Benjamin A. Borchelt [22] July 1971 AssistantExaminer-H. J. Tudor [21] Appl. No; 160,693 Attorney-Thomas H. Whaley etal.

[52] US. Cl. 340/12 R, 181/.5 H [57] ABSTRACT [51] Int. Cl. 1104b 13/00[58] Field of Search 3401s, 10, l2, 14; A mpmsed gas Wang 3 Isl/5 Hwater. It has a floating-action piston controlled by an auxiliary pistonfor releasing a compressed gas charge {56] Reknnm Cit suddenly. It alsoshapes the discharge gas pattern in the UNITED STATES PATENTS water toreduce secondary bubble pulse action. 3,276,534 l0/1966 Ewing et a].l81/.5 H 14 Claims, 3 Drawing Figures FIG. 1

PAIENIE am 3 v ms 3,750.09.

sum 2 or 2 FIG.

COMPRESSED GAS SEISMIC ENERGY GENERATOR BACKGROUND OF THE INVENTION I.Field of the Invention This invention concerns generation of seismicenergy, in general. More specifically, it relates to the structure of acompressed gas seismic gun for use in underwater seismic exploration.

2. Description of the Prior Art While it has been found that a seismicair gun for creating repeatable acoustic energy signals is feasible. theapparatus heretofore known has been found to have a major drawback. Suchdrawback relates to the same conditions that are created by an expolsionunder water, namely, the creation of a so-called bubble pulse. The gasbubble produces a secondary seismic energy pulse, by reason of thecollapse and re-expansion of the gas bubble first formed under water.

The primary seismic energy pulse generated by air gun structuresheretofore known, have not difiered substantially from the pulseconfiguration that was found objectionable, as noted above, in that asecondary bubble pulse follows some milliseconds in time after theinitial expansion and so overlapping and confusing indications on aseismic record. This is especially true in reflection seismicoperations. Consequently, it is an object of this invention to provideimproved air gun structure that substantially eliminates any secondaryseismic energy that tends to confuse a reflection or other type ofseismic record.

SUMMARY OF THE INVENTION Briefly, the invention concerns a compressedgas type of seismic energy generator. It relates to a combination with ahigh-pressure chamber for containing an energy pulse charge, a pistonfor closing one end of said chamber, and an auxiliary chamber forholding highpressure gas to apply a greater force to said piston whileit contains said energy pulse charge. In connection with the foregoingcombination, the invention relates to the improvement that comprisesmeans for instantaneously discharging said primary energy pulse chargewithout creating any substantial secondary bubble pulse generation.

Again briefly, the invention concerns a seismic energy generator adaptedfor use in a body of water. It comprises, in combination, a firstchamber containing a charge of high-pressure gas, a first piston forclosing an end wall of said first chamber. It also comprises arelatively small cross-sectional area passage for charging said firstchamber, and a discharge port located at said piston end wall of saidfirst chamber. Said discharge port has a flattened cross-sectional area,with a ratio of major-to-minor axes exceeding three to one.

Once more, briefly, the invention concerns a seismic energy generatoradapted for use in a body of water, which comprises in combination, afirst chamber for containing a predetermined volume charge ofhighpressure gas. It also comprises a first floating piston, as well asmeans for mounting said first piston for longitudinal movement from oneposition for closing an end wall of said first chamber to anotherposition. It also comprises a relatively small crosssection area passagefor charging said first chamber, and a plurality of discharge portslocated at said piston end wall and connected to said first chamber whensaid first piston is in said other position. The said ports are narrowslits with a circumferential-to-axial ratio of at least three to one,and it comprises an auxiliary chamber located at the other end of saidfirst floating piston. The effective area of said floating piston atsaid auxiliary chamber end is greater than the effective area at saidfirst chamber end. The invention also comprises means for filling saidauxiliary chamber with said high-pressure gas including a restrictedpassage, and an auxiliary floating piston constructed of relativelylight metal. as well as means for mounting said auxiliary piston forlongitudinal movement from one position for closing said auxiliarychamber to another position. It also comprises a plurality of exhaustchambers adjacent to said auxiliary piston and connected tsaid auxiliarychamber when said auxiliary piston is in said other position. The saidexhaust chambers have a total volume at least equal to the volume ofsaid auxiliary chamber. The combination also comprises a plurality ofcheck valves for preventing entering of water into said exhaustchambers, a solenoid-actuated three-way valve, and means for connectingsaid valve to alternatively control application of said high-pressuregas to one side of said auxiliary piston or cutting off said applicationwhile connecting said one side of the auxiliary piston to exhaust.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects andbenefits of the invention will be more fully set forth below inconnection with the best mode contemplated by the inventor of carryingout the invention, and in connection with which there are illustrationsprovided in the drawings, wherein FIG. 1 is a longitudinal view, partlyin cross-section, illustrating a generator according to the invention;

FIG. 2 is an enlarged cross-sectional view of the control valve of thegenerator illustrated in FIG. 1; and

FIG. 3 is a transverse cross-section view taken along the lines 33 ofFIG. 1, looking in the direction of the arrows.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to all of the figuresof the drawings and, first of all, to FIG. I, it will be observed thatthere is a seismic air gun 10 which has a first chamber II which iscontained in a thick-walled cylindrical shaped cap 12. The chamber 11will contain a charge of highpressure gas, e.g., compressed air. It mayvary in volume quite considerably depneding upon the total energydesired for a given seismic energy pulse. Thus, it would be thelongitudinal dimensions of cap 12 that would usually be varied in orderto create larger-sized chambers, as desired.

The compressed air for charging chamber 11 may be obtained from anyfeasible compressor (not shown). When the gun It) is in use, thecompressed air would be transmitted to the gun through a flexible hose(not shown) that would be attached to a connector 16. Connector 16 isthreadably attached into the upper end (as viewed in FIG. I) of ahousing 17 of the gun ill to which the cap member 12 is connected.

The high-pressure air wil be transmitted through the hose (not shown)via the connector 16 and internal piping and passageways which include apipe 20, a T- joint 21, and another pipe 22 which is connected to aninternal passage 23 in a solid body section 25 of the tool by a threadedconnector 24. The passageways continue through a connected passage 28that extends through a connecting body portion 29 that, in turn, joinsthe cap 12 to the body section 25.

The chamber 11 is formed with an open end by the structure of thecylindrical cap 12. Such open end is facing upward, as viewed in thedrawing, and it is closed by a floating-action piston 33 when the latteris in the lowermost position, as illustrated in FIG. I. In closing thechamber 11, piston 33 seats upon an O-ring seating element 34 that islocated in a groove at the upper edge of a short cylindrical sleeve 35.

The sleeve 35 is mounted for limited axial sliding ac tion within acylindrical section 38 on the interior of the connecting body portion 29of the tool 10. The sleeve 35 is maintained against leakage of thecompressed air around the outside thereof, by providing an O-ring 39.Also, the sleeve 35 is mounted with a spring bias upward (as viewed inthe drawing) to keep the piston 33 seated during the first portion ofmovement of the piston away from its lowermost position in order to helpsharpen the beginning of the generated pulse. The biasing of sleeve 35may be accomplished in any feasible manner, e.g., by having ring 42 thathas a plurality of springs 43 supported therein and that bear againstthe lower edge of the sleeve 35. The ring 42 may be mounted in anyfeasible manner and it is fixed in rela tion to the body 29 of the gunl0, e.g., by being fitted into a complementary groove 44 on the interiorof the body 29. It is held securely in place by having a threaded ring47 that fits beneath (as viewed in the drawing) the ring 42 with awasher 48 between them.

Piston 33 is mounted for so-called floating action within a cylinder 52which is located concentrically on the inside of the body 29. The pistonis sealed to prevent any leakage of compressed air around the edgesthereof by means of an O-ring 53. in addition, there is a guide ring 54to ensure smooth action of the longitudinal movement of the piston.

It will be noted that piston 33 has a compound structure to provide amain body portion 57 with a cap element 58. The cap 58 is constructed ofrelatively tough ma-terial to withstand pounding action as the piston isdriven up from the illustrated position against the top of thecylindrical chamber 52, when the compressed air charge in chamber 1] isexhausted.

When the piston 33 moves up away from its seated position (illustratedin FIG. 1), it releases the charge of compressed air that is containedin chamber 11 out through three transverse, or radial ports 61, 62 and63 (see FIG. 3) through which the compressed air charge is released.However, it will be observed that the diameter of the cylindricalchamber 52 is greater than that of the bottom (as viewed in the drawing)of piston 33. Consequently, there is a net force applied downward whichholds the piston firmly seated against the O-ring 34 so long as thecompressed air is contained both above and below the piston.

It will be noted that the ports 61, 62 and 63 have a flattenedconfiguration in cross-sectional area so that the ratio of thecircumferential dimension to the axial dimension is quite substantialand, preferably, at least three to one. This structure for the exhaustports of the gun creates a sharp-edged discharge pattern, and suchpattern is thought to be a substantial factor in the ability of the gunto provide a seismic energy pulse which is substantially without anysecondary bubble pulse energy. In addition, it is believed that othercontributing factors include the rapid action that is obtained with thecontrol elements to be described below. Also, the construction is suchthat the amount of water which must be bodily displaced from within thebody of the gun is minimized.

Located at the other end of piston 33 from that which closes chamber ll,i.e., above as viewed in the drawing, there is an auxiliary chamber 67.It will contain the high-pressure air as the tool is charged, prior tothe commencement of a seismic pulse generation. The operation willappear more fully hereafter. It may be noted that there is an internalpassage 68 that connects with the passage 23 inside of the body section25. Also, there is a restriction 69 adjacent to the point where thepassage 68 connects into the chamber 67.

Above the auxiliary chamber 67 (when viewed as illustrated in thedrawings), there is an auxiliary piston 72 that is preferablyconstructed of a light metal, e.g., aluminum, in order to reduce itsinertia and promote more rapid action thereof. The piston 72 is locatedfor floating action within a cylindrical walled, axially located opening73 which is situated axially within the body section 25 of the tool.Surrounding the cylindrical opening 73, there are a plurality ofradially situated exhaust chambers 74. They extend around, and areconnected into the cylindrical opening 73 at the lower end thereof. Thesize of these chambers 74 is such that the total volume of all of themadded together is at least equal to the volume of the chamber 67 whenthe primary piston 33 is in its lowermost position, as shown.

It will be noted that piston 72 has a reduced diameter end portion 77that seats upon an O-ring 78 to seal off the auxiliary chamber 67 whenpiston 72 is in its lowermost position (as shown in FIG. I). It will beobserved that the arrangement is such as to open a connection from thechamber 67 to the exhaust chambers 74, whenever piston 72 moves up offthe seat created by O-ring 78.

In order to provide a necessary seal between the walls of opening 73 andthe piston 72, there is another O-ring 79, as illustrated. Thepositioning of piston 72 is controlled by application of compressed airto a space 82 at the upper end of the cylindrical opening 73.introduction of such compressed air is controlled by a solenoid-actuatedthree-way valve 88, that has the details thereof shown more clearly inFIG. 2. There is an exhaust line for the valve 82 that includes a pipe89 which leads from an exhuast port of the valve to a check valve 90.The check valve acts to release discharged compressed air whilepreventing any reentry of water from outside the gun. This type of checkvalve simply employs a plurality of radial ports 87 which are closed bya flexible O-ring 86. Any excess of pressure on the inside of the valve90 will expand the 0-ring 86 andopen the valve for exhaust or outwardflow, while equal or reverse pressures will leave the O-ring seatedagainst the ports 87 to prevent reverse flow.

Referring to FIG. 2, it will be noted that the valve 88 includes aplunger 93 which is spring-biased into the position illustrated, by acoil spring 94. There is an internal passageway 97 located axiallywithin the plunger 93, and it connects a space 96 above the plunger tothe opening of a lip or nozzle 98 located at the other end of theplunger. Consequently, when the plunger 93 is in the illustratedposition, there is an open passage for compressed air to flow throughfrom an upper passageway 101 and past a valve seat 102, around thespring 94 to connect with upper branches 103 of the passage 97. Thus,air may be introduced into the space 82 via a passage 105 (FIG. 2) thatmay, in the alternative, be connected with an outlet port 106 (of valve88) which connects into the pipe 89, FIG. 1 for exhausting compressedair from space 82 FIG. 2, when the valve 88 has been energized.

There is a coil 110 that is schematically illustrated which acts whenenergized to pull the plunger 93 up against the coil spring 94 whichbiases the plunger down into the position illustrated in FIG. 2. Theenergization of the coil 110 will, thus, cause a solid pointed tip 111on the plunger 93 to seat against the valve 102 and close off passageway101. At the same time, a lower extension 114 of the plunger 93 is raisedup so that the nozzle 98 is lifted off a valve seat 115. This opens aconnection from passage 105 via port 106 to pipe 89 (FIG. 1) that leadsto exhaust via the check valve 90.

it may be noted that there is an O-ring H8 that acts between the outsideof extension 114 of the plunger 93 and a body portion 119 of the valve88.

It will be observed in FIG. 1 that there is pipe 120 that leads from theT-joint 21 to an elbow connector [23, which together make a passage forhigh-pressure air from the compressed air base connector 16 to thepassageway 101 at the inlet end of the valve 88.

OPERATION The operation of the particular air gun which was describedabove, may be followed commencing with the introduction of a gas underpressure. e.g., compressed air, into the gun via a flexible hose (notshown) which leads to the connector 16 on the gun. This compressed airwill flow through the pipe 20 and via Tjoint 21 and then throughparallel paths including the pipe 22 (for charging the main andauxiliary chambers) while, at the same time, flowing through pipe 120 toapply compressed air to the inlet port of the threeway valve 88. Itcontinues through the valve 88, when the solenoid is not energized, toone side of the piston 72, i.e., space 82, for controlling the charge inauxiliary chamber 67. The path through the valve is shown in FIG. 2, andit may be traced from the internal passage of the elbow 123, throughpassageway and past seat 102. Then it continues via space 96 and throughbranches 103 to passageway 97 and to the passage 105 that connects intospace 82.

It will be noted that the compressed air flowing in the foregoing pathsto fill space 82 is relatively unimpeded and will build pressure morequickly than the compressed air flowing through pipe 22 and passage 68into chamber 67. This is because of the restriction 69 that holds backthe rate of flow over the latter path.

Consequently, as the tool is charged, the control piston 72 will bepositively seated into the position illustrated in FIG. 1 closing theauxiliary chamber 67. As indicated, this is caused by the faster actionof compressed air flow through the internal passages of sole noid valve88 as compared with the flow from the source of supply into chamber 67via the restriction 69. The positive seating is maintained after flow ofthe compressed air has ceased by reason of the area of the piston 72 (inspace 82), which is greater than the area of the piston where it seatson the O-ring 78. The latter is at the bottom of the smaller diameterend portion 77 of the piston 72.

At the same time as the foregoing control portions of the gun are beingcharged with compressed air, it will flow through the parallel path ofpassageways 23 and 28 into the main chamber 11. Because of the volume ofchamber 11, as compared with the volume of chamber 67, the main piston33 will have pressure build-up faster in the auxiliary chamber 67 above(as viewed in FIG. 1) the piston so that it will be seated firmly intothe illustrated position. Also, once the pressures have equalized, itwill be firmly held with lower edge of the piston seated in apressure-tight manner against O-ring 34 by reason of the dimensions ofthe whole piston 33. As has been indicated above, the piston 33 has agreater ef-fective area at the top (as illustrated in FIG. 1) relativeto the effective area at the bottom where it seats on O-ring 34 to closethe end wall of main chamber 11.

Now, when it is desired to generate a sudden and short-duration seismicenergy pulse, the coil 110 of solenoid valve 88 will be energized, andthis will pull up the plunger 93 so as to close off high-pressure air atvalve seat 102 see FIG. 2). Simultaneously, it will open a connectionbetween passage 105 and exhaust port 106 of the three-way valve 88.

The result of the foregoing action in the valve causes the auxiliarypiston 72 to be suddenly moved upward within the cylinder walls 73 and,consequently, to open a connection between auxiliary chamber 67 and theplurality of exhaust chambers 74. As was noted above, the total volumeof chambers 74 is at least equal to the volume of chamber 67 and,consequently, there is a sudden drop in the pressure within chamber 67to half or less of the original pressure. Then the pressure willcontinue to drop quite rapidly down to the pressure existing outside ofthe tool. The latter is by reason of the air exhausting from each of theexhaust chambers 74 via a plurality of check valves 126 which areprovided to keep the water out of the exhaust chambers. These checkvalves 126 might take different forms but are preferably like the checkvalve that was described above. Thus, each valve 126 has a stretchableO-ring 127 that closes the ring of exhaust ports 128 against any reverseflow of water or other fluid into the chambers 74, while expanding andopening these ports to permit exhaust flow of compressed air from thechambers so long as the pressure exceeds that outside the tool.

When the pressure in chamber 67 is suddenly reduced, as just describedabove, it causes the main piston 33 to be accelerated at a high rate andto be lifted very rapidly off of its seat against the O-ring 34. Thesharpness of the opening action for the main chamber 11 is enhanced bythe dynamic seal created by the structure of the sleeve 35 and ring 42with springs 43 and related elements, which were described above. Thus,as soon as the sleeve 35, which carries the O-ring 34, reaches itsuppermost position, the compressed air charged in chamber 11 will beinstantaneously released out through the discharge ports 61, 62 and 63.This discharge of the compressed air from chamber 11 will generate thedesired primary seismic energy pulse in the water, and at least in partby reason of the dimensions of the ports 61, 62 and 63, this energypulse will have any secondary or delayed bubble pulse action thereof,substantially eliminated.

While a particular embodiment of the invention has been described abovein considerable detail in accordance with the applicable statues. thisis not to be taken as in any way limiting the invention but merely asbeing descriptive thereof.

What we claim is:

l. in a compressed gas type of seismic energy generator, in combinationwith a high pressure chamber for containing an energy pulse charge apiston for closing one end of said chamber, and an auxiliary chamber forholding high pressure gas to apply a greater force to said piston, whileit contains the energy pulse charge, the improvement comprising meansfor instantaneously discharging said energy pulse charge withoutcreating substantial secondary bubble pulse generation,

said means for discharging said energy pulse comprising outlet portmeans connected to said highpressure chamber and having a large ratio oflateralto longitudinal dimensions for forming a sharp-edged dischargepattern,

an auxiliary piston, and

means associated with said auxiliary piston for actuating saidfirstnamed piston to hold and release said energy pulse charge.

2. In a seismic generator according to claim 1, said discharging meansalso comprising:

exhaust chamber means connected to said auxiliary chamber when saidauxiliary piston is in the released position, and

check valve means for preventing fluid flow-back from the exterior ofsaid generator into said exhaust chamber means.

3. The invention according to claim 2, wherein said exhaust chambermeans has a volume at least equal to the volume of said auxiliarychamber.

4. The invention according to claim 2, further comprising:

a control chamber for holding high-pressure gas to apply a greater forceto said auxiliary piston when it is holding said auxiliary chamberclosed, and

valve means for alternatively connecting a highpressure gas line to saidcontrol chamber or shutting off said high-pressure gas line whilesimultaneously connecting said control chamber to exhaust.

5. The invention according to claim 4, wherein said exhaust chambermeans has a volume at least equal to the volume of said auxiliarychamber.

6. The invention according to claim 2, wherein said auxiliary piston isconstructed of relatively light material.

7. The invention according to claim 3, wherein said auxiliary piston isconstructed of a relative-[y light material.

8. The invention according to claim 5, wherein said auxiliary piston isconstructed of a relative-ly light material.

9. A seismc energy generator adapted for use in a body of waterconprising in combination,

a first chamber for containing a charge of highpressure gas,

a first piston for closing an end wall of said first chamber,

a relatively small cross-section area passage for charging said firstchamber,

a discharge port located at said piston end wall of said first chamber,

said discharge port having a flattened cross-sectional area with a ratioof major-to-minor axes exceeding three to one,

an auxiliary chamber located at the other end of said first piston,

said auxiliary chamber having an effective area in contact with saidfirst piston greater than the area of said end wall,

means for filling said auxiliary chamber with said high-pressure gas,and

auxiliary piston means for closing said auxiliary chamber when in oneposition, and for connecting said auxiliary chamber to an exhaustchamber when in another position.

10. A seismic energy generator according to claim 9,

wherein said exhaust chamber has a volume at least equal to the volumeof said auxiliary chamber.

11. A seismic energy generator according to claim 10, furthercomprising:

check valve means for preventing entry of water into said exhaustchamber.

12. A seismic energy generator according to claim 11, furthercomprising:

a restricted passage for permitting filling of said auxiliary chamberwith said high-pressure gas after said auxiliary piston has closed saidauxiliary chamber, and

three-way valve means for controlling acutation of said auxiliary pistonmeans from one position to the other.

13. A seismic energy generator according to claim 12, wherein saidauxiliary piston means is constructed of a relatively light material,and

said three-way valve means comprises a solenoidactuated plunger foralternatively connecting said high-pressure gas to one side of saidauxiliary piston means or cutting off said high-pressure gas, andconnecting said one side of auxiliary piston means to exhaust.

14. A seismic energy generator adapted for use in a body of water,comprising in combination a first chamber for containing a predeterminedvolume charge of high-pressure gas,

a first floating piston,

means for mounting said first piston for longitudinal movement from oneposition for closing an end wall of said first chamber to anotherposition,

a relatively small cross-section area passage for charging said firstchamber,

a plurality of discharge ports located at said piston end wall andconnected to said first chamber when said first piston is in said otherposition,

said ports being narrow slits with a circumferentialto-axis ratio of atleast three to one,

an auxiliary chamber located at the other end of said first floatingpiston,

the effective area of said floating piston at said auxiliary chamber endbeing greater than the effective area at said first chamber end,

means for filling said auxiliary chamber with said high-pressure gasincluding a restricted passage,

an auxiliary floating piston constructed of a relatively light metal,

a plurality of check valves for preventing entry of water into saidexhaust chambers.

in solenoid-actuated three-way valve. and

means for connecting said valve to alternatively control application ofsaid high-pressure gas to one side of said auxiliary piston or cuttingoffsaid application olf said connecting said one side of the auxiliarypiston to exhaust.

# i i i U

1. In a compressed gas type of seismic energy generator, in combinationwith a high pressure chamber for containing an energy pulse charge apiston for closing one end of said chamber, and an auxiliary chamber forholding high pressure gas to apply a greater force to said piston, whileit contains the energy pulse charge, the improvement comprising meansfor instantaneously discharging said energy pulse charge withoutcreating substantial secondary bubble pulse generation, said means fordischarging said energy pulse comprising outlet port means connected tosaid high-pressure chamber and having a large ratio oflateral-to-longitudinal dimensions for forming a sharp-edged dischargepattern, an auxiliary piston, and means associated with said auxiliarypiston for actuating said first-named piston to hold and release saidenergy pulse charge.
 2. In a seismic generator according to claim 1,said discharging means also comprising: exhaust chamber means connectedto said auxiliary chamber when said auxiliary piston is in the releasedposition, and check valve means for preventing fluid flow-back from theexterior of said generator into said exhaust chamber means.
 3. Theinvention according to claim 2, wherein said exhaust chamber means has avolume at least equal to the volume of said auxiliary chamber.
 4. Theinvention according to claim 2, further comprising: a control chamberfor holding high-pressure gas to apply a greater force to said auxiliarypiston when it is holding said auxiliary chamber closed, and valve meansfor alternatively connecting a high-pressure gas line to said controlchamber or shutting off said high-pressure gas line while simultaneouslyconnecting said control chamber to exhaust.
 5. The invention accordingto claim 4, wherein said exhaust chamber means has a volume at leastequal to the volume of said auxiliary chamber.
 6. The inventionaccording to claim 2, wherein said auxiliary piston is constructed ofrelatively light material.
 7. The invention according to claim 3,wherein said auxiliary piston is constructed of a relative-ly lightmaterial.
 8. The invention according to claim 5, wherein saId auxiliarypiston is constructed of a relative-ly light material.
 9. A seismcenergy generator adapted for use in a body of water conprising incombination, a first chamber for containing a charge of high-pressuregas, a first piston for closing an end wall of said first chamber, arelatively small cross-section area passage for charging said firstchamber, a discharge port located at said piston end wall of said firstchamber, said discharge port having a flattened cross-sectional areawith a ratio of major-to-minor axes exceeding three to one, an auxiliarychamber located at the other end of said first piston, said auxiliarychamber having an effective area in contact with said first pistongreater than the area of said end wall, means for filling said auxiliarychamber with said high-pressure gas, and auxiliary piston means forclosing said auxiliary chamber when in one position, and for connectingsaid auxiliary chamber to an exhaust chamber when in another position.10. A seismic energy generator according to claim 9, wherein saidexhaust chamber has a volume at least equal to the volume of saidauxiliary chamber.
 11. A seismic energy generator according to claim 10,further comprising: check valve means for preventing entry of water intosaid exhaust chamber.
 12. A seismic energy generator according to claim11, further comprising: a restricted passage for permitting filling ofsaid auxiliary chamber with said high-pressure gas after said auxiliarypiston has closed said auxiliary chamber, and three-way valve means forcontrolling acutation of said auxiliary piston means from one positionto the other.
 13. A seismic energy generator according to claim 12,wherein said auxiliary piston means is constructed of a relatively lightmaterial, and said three-way valve means comprises a solenoid-actuatedplunger for alternatively connecting said high-pressure gas to one sideof said auxiliary piston means or cutting off said high-pressure gas,and connecting said one side of auxiliary piston means to exhaust.
 14. Aseismic energy generator adapted for use in a body of water, comprisingin combination a first chamber for containing a predetermined volumecharge of high-pressure gas, a first floating piston, means for mountingsaid first piston for longitudinal movement from one position forclosing an end wall of said first chamber to another position, arelatively small cross-section area passage for charging said firstchamber, a plurality of discharge ports located at said piston end walland connected to said first chamber when said first piston is in saidother position, said ports being narrow slits with acircumferential-to-axis ratio of at least three to one, an auxiliarychamber located at the other end of said first floating piston, theeffective area of said floating piston at said auxiliary chamber endbeing greater than the effective area at said first chamber end, meansfor filling said auxiliary chamber with said high-pressure gas includinga restricted passage, an auxiliary floating piston constructed of arelatively light metal, means for mounting said auxiliary piston forlongitudinal movement from one position for closing said auxiliarychamber to another position, a plurality of exhaust chambers adjacent tosaid auxiliary piston and connected to said auxiliary chamber when saidauxiliary piston is in said other position, said exhaust chambers havinga total volume greater than the volume of said auxiliary chamber, aplurality of check valves for preventing entry of water into saidexhaust chambers, a solenoid-actuated three-way valve, and means forconnecting said valve to alternatively control application of saidhigh-pressure gas to one side of said auxiliary piston or cuttingoffsaid application off said connecting said one side of the auxiliarypiston to exhaust.